Bipolar interrogation for magnetostrictive transducers

ABSTRACT

A magnetostrictive-based sensor is disclosed which obtains higher return signals through the use of multiple consecutive input pulses

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of and claims priority of U.S.patent application Ser. No. 10/419,447, filed Apr. 21, 2003, which isU.S. Pat. No. 7,292,025, which issued Nov. 6, 2007, the content of whichis hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to magnet-based sensors and in particularmagnet-based magnetostrictive sensors.

2. Description of the Art

Magnetostrictive transducers having elongated waveguides that carrytorsional strain waves induced in the waveguide when current pulses areapplied along the waveguide through a magnetic field are well known inthe art. A typical linear distance measuring device using a movablemagnet that interacts with the waveguide when current pulses areprovided along the waveguide is shown in U.S. Pat. No. 3,898,555.

Devices of the prior art of the sort shown in U.S. Pat. No. 3,898,555also have the sensor element in a housing which also houses theelectronics to at least generate the pulse and receive the returnsignal. The amplitude of the return signal detected from the acousticalstrain pulse is, as well known in the art, affected by many parameters.These parameters include the position magnet strength, waveguidequality, temperature, waveguide interrogation current, and assemblytolerances.

Several types of magnetic-based sensors are available for measuringlinear or rotary position. Magnetic-based sensors have an advantage inthat they provide non-contact sensing; so there are no parts to wearout. Examples of magnetic-based sensors are LVDTs, inductive sleevesensors, and magnetostrictive sensors.

Magnetostrictive transducers require that their waveguide beinterrogated with electric current. This magnetically energizes thewaveguide, thereby launching the ultrasonic strain pulse that isdetected at the end of the unit. When the strain pulse is converted toan electrical signal, it is referred to as the “return signal.” The timebetween the interrogation pulse and the detection of the return signaldefines location of position magnet.

Normally, the interrogation current in the waveguide flows in onedirection for a short period of time (one to three microseconds) priorto detection at the return signal.

It is an object of the present invention to combine magnetostrictiveinterrogation pulses additionally to increase the amplitude of thereturn signal.

It is another object of the present invention to provide amagnetostrictive interrogation pulse voltage with a lower voltage powersupply.

SUMMARY OF THE INVENTION

The present invention relates to a magnetostrictive device whereinmultiple interrogation pulses originate from an interrogation source insequence without delay time between the pulses. Eliminating substantialdelay between positive and negative going current pulses induce aresonance in the waveguide for constructively additive return signalsproducing a resultant return signal which is of much higher voltagestrength.

The interrogation current flows first in one direction and then isreversed and flows in the opposite direction. Preferably theinterrogation current flows in the first direction as a third pulseimmediately following the second pulse. The timing of these currentflows, as well as the synchronization, are adjusted so that resonancebetween the two parts of the return signal is obtained. This results ina resonated return signal that is about twice as large as that which canbe obtained with only a single direction interrogation pulse.

DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention, reference should be had to the following figures in whichlike parts are given like reference numerals and wherein:

FIG. 1 is a schematic view of a linear magnetostrictive position sensorof the present invention;

FIG. 2 is an illustration of interrogation pulses of opposing polarity;

FIG. 3 is an illustration of the return signal from the magnetostrictivesystem in response to the interrogation pulse sequence of FIG. 2;

FIG. 4 is an illustration of interrogation pulses for themagnetostrictive system without spacing between the pulses;

FIG. 5 is an illustration of the return signal of the magnetostrictivesystem in response to the interrogation pulses of FIG. 4; and

FIG. 6 is a schematic of an illustrative circuit which is used to createthe pulses of FIG. 4.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

As shown in FIG. 1, there is a typical assembly of a waveguide formagnetostrictive detection of a position of a magnet in close proximityto the waveguide. As shown in FIG. 1, a waveguide 10 extends from aninterrogation source 20 through a pickup head 30 to its termination end40. At its termination end 40, a return wire 50 is connected to the end40 of waveguide 10 and also extends to pickup head 30 and from pickuphead 30 to interrogation source 20. A position magnet 60 is mountedaround or otherwise in close proximity to the return wire 50 andwaveguide 10. Thus, in the prior art, the interrogation source, such asinterrogation source 20, would introduce a current onto the waveguide 10in the form of a single current pulse which would be returned by returnwire 50 and the current pulse in interaction with the position magnet 60would yield at pickup head 30 a detectable signal indicating theposition of the position magnet 60 along waveguide 10. However, as shownin FIGS. 2 and 3, there is an effective resonance which is not known inthe art.

As shown in FIG. 2, there is an interrogation pulse 100. Typically,interrogation pulse 100 is the only pulse introduced into a waveguide 10as discussed above. However, as shown in FIG. 2, the current pulse doesnot have to be limited to pulse 100 but can continue as a negative goingpulse 200 and maybe followed by a positive going pulse 300. This is notdone in the art at the present time to the knowledge of the inventor.

FIG. 3 shows the result on return pulses in a magnetostrictive system ofhaving current pulses flow in opposite directions. If the current pulsesare as shown in FIG. 2, the return pulses are as shown in FIG. 3. Thesereturn pulses correspond to the interrogation pulses 100, 200, and 300and are indicated in FIG. 3 as return signals 400, 500, and 600,respectively. Return signal 500 is opposite polarity from return signals400, 600, as the input pulse 200 is opposite in polarity to input pulses100, 300, respectively. However, the input pulses 100, 200, 300 may bespaced in time differently than is shown in FIG. 2 by adjusting when thesignals are positive and negative going.

In FIG. 4, the interrogation pulses 100, 200, 300 no longer have anydelay time between them, as they did in FIG. 2, but are substantiallyone on top of the other. By doing so, a resonance is induced in thewaveguide 10 so that the return signals as shown in FIG. 5 areconstructively additive for a return signal 700, which has a much highervoltage strength (approximately twice that of the individual returnpulses of FIG. 3) to help in, first, detection of the return signal and,second, to improve the signal-to-noise ratio of the signal.

FIG. 6 shows an illustrative circuit that may be used to create thepulses. As shown in FIG. 6, the circuit is essentially a bridge drivercircuit 910 to generate bi-directional current pulses. Waveguide 10 isconnected to the output 900 of the bridge circuit, and the return wire50 is connected to the other output 1000 of the bridge circuit. A timingcircuit 905 well known in the art is connected to the input end of thebridge circuit 910, driving the bridge circuit 910 to alternativelyproduce the positive and negative going current signals.

Additional superiorities for the bipolar interrogation pulses additivelyraising the return signal are:

-   1. Being able to achieve a specified output from the waveguide using    a lower voltage supply, such as using the lowest voltage possible in    order to supply the waveguide to reach the desired voltage. This is    an advantage for making an intrinsically safe sensor, wherein a    higher input voltage that more easily can ignite the atmosphere if a    spark occurs is no longer needed.-   2. If the power supply voltage for the input pulse is limited    because of the application, such as a mobile unit, the higher output    that one can obtain from that given voltage also allows one to    achieve a better signal-to-noise ratio.

Because many varying and different embodiments may be made within thescope of the invention concept taught herein which may involve manymodifications in the embodiments herein detailed in accordance with thedescriptive requirements of the law, it is to be understood that thedetails herein are to be interpreted as illustrative and not in alimiting sense.

1. A magnetostrictive transducer, comprising: a magnetostrictivewaveguide; a return wire connected to the magnetostrictive waveguide; amagnet movable in close proximity to the magnetostrictive waveguide; anda bipolar driver circuit coupled to the magnetostrictive waveguide, saidbipolar driver circuit configured to generate at least two consecutivecurrent pulses of opposite polarity, wherein the current pulses ofopposite polarity are timed to generate a return pulse along themagnetostrictive waveguide that has an amplitude larger than if thereturn pulse was from a single current pulse.
 2. The magnetostrictivetransducer of claim 1, wherein the bipolar driver circuit comprises abridge driver circuit.
 3. The magnetostrictive transducer of claim 1,wherein the bipolar driver circuit comprises an intrinsically safecircuit.
 4. The magnetostrictive transducer of claim 1 wherein themagnetostrictive waveguide comprises a linear magnetostrictive positionsensor.
 5. The magnetostrictive transducer of claim 4 further comprisinga termination end, and the magnetostrictive waveguide and the returnwire connect to one another at the termination end.
 6. Amagnetostrictive transducer, comprising: a magnetostrictive waveguide; areturn wire connected to the magnetostrictive waveguide; a magnetmovable in close Proximity to the magnetostrictive waveguide; and abipolar driver circuit coupled to the magnetostrictive waveguide, saidbipolar driver circuit configured to generate at least two consecutivecurrent pulses of opposite polarity wherein the magnetostrictivewaveguide comprises a resonance that generates the return pulse suchthat the return pulse is constructively additive.
 7. Themagnetostrictive transducer of claim 6 further comprising a terminationend, and the magnetostrictive waveguide and the return wire connect toone another at the termination end.
 8. The magnetostrictive transducerof claim 6 further comprising a pickup head and wherein themagnetostrictive waveguide extends through the pickup head.
 9. Amagnetostrictive transducer, comprising: a magnetostrictive waveguidewith a resonance; a magnet movable in close proximity to themagnetostrictive waveguide; and a bipolar driver circuit coupled to themagnetostrictive waveguide, said bipolar driver circuit configured togenerate at least two consecutive current pulses of opposite polaritythat are timed such that the resonance generates a constructivelyadditive return pulse.
 10. The magnetostrictive transducer of claim 9,wherein the bipolar driver circuit comprises a bridge driver circuit.11. The magnetostrictive transducer of claim 9, wherein the bipolardriver circuit comprises an intrinsically safe circuit.
 12. Themagnetostrictive transducer of claim 9 wherein the current pulses ofopposite polarity are timed to generate a return pulse along themagnetostrictive waveguide that has an amplitude larger than if thereturn pulse was from a single current pulse.
 13. The magnetostrictivetransducer of claim 9 wherein the magnetostrictive waveguide comprises alinear magnetostrictive position sensor.
 14. The magnetostrictivetransducer of claim 9 further comprising a return wire and a terminationend, and the magnetostrictive waveguide and the return wire connect toone another at the termination end.
 15. The magnetostrictive transducerof claim 14 wherein the magnetostrictive waveguide comprises a linearmagnetostrictive position sensor.